This historical evaluation of the Advanced Research Projects Agency (ARPA) as an R&D management institution was commissioned by ARPA in recognition of the fact that remarkably little in the way of an official recordor institutional memory had been established during its seventeen year lifetime. From Agency Directors to program managers, the turnover in its leadership has been rapid by most bureaucratic standards, thus eroding first hand knowledge of ARPA's role and activities rather quickly. Conceived as a unique management organization chartered to concentrate on advanced research within the Department of Defense, this very uniqueness has frequently been questioned. Virtually every ARPA Director, and most ARPA personnel at all levels, have encountered friendly and not-so-friendly why ARPA? and what is ARPA? questions throughout its history. This report seeks to explain some of the whys and whats. For the most part, the study ends in 1972 when ARPA was designated a Defense Agency. This date was arbitrarily chosen. In instances where events or programs started in earlier periods extend beyond 1972, they have been pursued a bit further for sake of completeness, but not past 1974.